The present invention is directed toward elongated imaging components and a method of making the components, and, more particularly, toward thin-walled, elastic sheaths for elongated imaging equipment and a method of making the same.
The use of intrabody medical equipment, such as endoscopes, catheters, and the like, for diagnostic and therapeutic indications is rapidly expanding. To improve performance, the equipment has been optimized to best accomplish the selected purpose. As an example, endoscopes have been optimized and refined so as to provide upper endoscopes for the examination of the esophagus, stomach, and duodenum, colonoscopes for examining the colon, angioscopes for examining blood vessels, bronchoscopes for examining bronchi, laparoscopes for examining the peritoneal cavity, arthroscopes for examining joints and joint spaces, nasopharygoscopes for examining the nasal passage and pharynx, and intubation scopes for examination of a person""s airway.
Optimization of intrabody medical equipment for such therapeutic and diagnostic procedures has resulted in sterile, inexpensive disposable components that are used alone or with non-disposable equipment. In the field of endoscopes, a conventional endoscope 10, shown in FIG. 1, has an insertion tube 12 connected at its proximal end 14 to a handle or control body 16. The insertion tube 12 is adapted to be inserted into a patient""s body cavity to perform a selected therapeutic or diagnostic procedure. The insertion tube 12 contains an imaging system 18 having optical fibers or the like extending along the length of the insertion tube and terminating at a viewing window 19 in the insertion tube""s distal end 20. The imaging system 18 conveys an image from the viewing window 19 to an eyepiece 22 on the control body 16 or to a monitor (not shown), so the user can see into a selected body cavity during an endoscopic procedure. The endoscope 10 is described in greater detail in U.S. Pat. No. Re 34,110 and U.S. Pat. No. 4,646,722, which are incorporated herein by reference.
Disposable endoscopic sheath assemblies are used to cover the insertion tube 12 and protect it from contaminating a patient during use. Accordingly, the sheath assemblies alleviate the problem and cost of cleaning and sterilizing the insertion tube 12 between endoscopic procedures. The sheaths and endoscopes are usable in medical applications and also in industrial applications, such as visually inspecting difficult to reach areas in an environment that could damage or contaminate the endoscope. As an example, a sheathed endoscope can be used in an industrial area wherein the sheath protects the endoscope""s insertion tube from adhesive or the like. As seen in FIG. 1, a conventional sheath assembly 24, shown partially cut away for illustrative purposes, includes a sheath 26 that surrounds the endoscope""s insertion tube 12. The sheath assembly 24 may also contain one or more working channels 32 that extend along the insertion tube 12 and that are adapted to receive conventional endoscopic accessories therethrough without allowing the endoscope to contaminate the accessories during the endoscopic procedure. The sheath 26 has a distal end portion 21 that includes an endcap 34 having a transparent window 28 positioned to cover the viewing window 19 at the insertion tube""s distal end 20 when the sheath assembly 24 is installed. The endcap 34 is sealably secured to the sheath""s distal end portion 21.
The sheath 26 and endcap 34 are commonly made from polymeric materials. The sheath 26 can be made from an inelastic polymer, such as PVC, acrylic, polycarbonate, polyethylene terephthalate or other thermoplastic polyesters, or can be made from an elastomeric material. Both materials presently have advantages and disadvantages.
Inelastic materials allow for thin-walled medical components that exhibit high strength and visible clarity. Using inelastic materials, the sheath 26 can be formed with a thin wall (measuring 0.003 inches or less) and a small diameter (such as 0.5 mm). Inelastic materials tend to be clearer than the elastic materials, and can thus provide better visibility with less distortion.
U.S. Pat. No. 5,443,781 to Saab teaches a method of forming an inelastic, disposable sheath with an integral, optically transparent window. Saab teaches forming the inelastic sheath by heating a sheet or film of optically transparent, inelastic, polymeric material until the material is malleable. As shown in FIG. 2, a mandrel 35 is thrust into the heated film 37 causing the film to stretch and to generally conform to the mandrel""s shape. As a result, the heated film 37 is formed into an inelastic closed-end sheath 39 having sidewalls 36, a flange or collar 38 at its open proximal end 40, and a closed distal end 42.
U.S. patent application Ser. No. 08/948,615, which is incorporated herein by reference, further teaches a method of forming an inelastic, endoscopic sheath for use on an insertion tube having a complex cross-sectional shape. The process applies a differential pressure to the outside and inside of the sheath during fabrication to conform the sheath to the shape of a mandrel. By selecting a mandrel with the proper complex shape, the end cap can closely receive the corresponding insertion tube.
Inelastic materials, however, have a number of disadvantages. Tight-fitting sheaths formed from inelastic materials may overly restrict bending when used with flexible insertion tubes. The insertion tube combined with the tight-fitting, inelastic sheath can only bend over a limited radius. If bent further, the sheath will either buckle, in the case of a thick-walled sheath, or the sheath material will become taught, in the case of a thin-walled sheath, preventing the insertion tube from bending further. Consequently, if the inelastic sheath is to be used in combination with a flexible endoscope, the sheath is typically either baggy or must contain bending features, such as accordion-like baffles or the like, as taught by Saab, to allow the insertion tube to sufficiently bend. Both baggy sheaths and these additional bending features add to the cross-sectional size of the sheath during use, which may result in additional pain or discomfort to the patient.
The sheath made from inelastic material cannot be stretched axially onto the insertion tube. As a result, the inelastic sheath does not provide axial tension in the sheath urging the transparent window of the sheath against and in alignment with the viewing window at the insertion tube""s distal end. To retain the transparent window in position, additional features, such as connectors or helical coils, are typically built into the sheath. These features add to the complexity and cost of the sheath.
Conventional elastic sheaths have been developed and used with imaging devices such as endoscopes to overcome the drawbacks associated with the inelastic sheaths described above and to provide additional benefits. As an example, conventional elastic sheaths are designed so the sheath will easily bend with the insertion tube without substantially affecting the insertion tube""s bending characteristics. The elastic sheath can also be stretched axially over the insertion tube to provide axial tension that retains the transparent window on the sheath against and in alignment with the viewing window at the insertion tube""s distal end. The elastic sheath can be designed to closely or tightly cover the insertion tube while still being able to bend with the insertion tube, so the elastic sheath does not need additional bending features.
Elastic materials, however, also have some disadvantages. First, conventional elastic sheaths are manufactured by extruding elastomeric material, that is, by pushing or forcing the elastomeric material through a die to form the desired structure. The extruded elastic sheaths, however, have manufacturing limits that restrict the minimum wall thickness of the sheath. Efforts toward manufacturing such a sheath have typically resulted in the extruded material collapsing or wrinkling during the process. As a result, the extruded elastic sheath must be made with a relatively thick wall (i.e., greater than 0.006 inches). The thicker the sheath wall in a tight-fitting sheath, the greater the resistance to bending.
Tight fitting, elastic sheaths can also be complex and expensive to install onto the insertion tube. The elastic materials commonly used to manufacture the sheath have high friction characteristics. As a result, it can be difficult to insert the insertion tube into the tight-fitting sheath because the insertion tube binds on the inner wall of the sheath. One solution is to make the sheath with a diameter considerably larger than the insertion tube, so the sheath is baggy when installed on the insertion tube. Baggy sheaths, however, are undesirable in many endoscopic procedures because the sheath can be twisted, bunched, or misaligned relative to the insertion tube during the procedure. The baggy sheath can also increase the diameter of the sheathed insertion tube, which can increase pain or discomfort to the patient. In another solution, a tight-fitting sheath and endoscope are specially designed to mate with a vacuum or inflation chamber (not shown) that radially expands the sheath while the insertion tube is inserted into the sheath. Once the insertion tube is fully inserted into the sheath, the vacuum or inflation pressure is removed and the sheath contracts to a size that fits closely over the insertion tube. The equipment needed for this installation process, however, as well as the time required to learn and perform the process, can significantly increase the cost of endoscopic procedures.
In the design of intrabody medical devices and accessories, including optical and non-optical devices, there is a need for components having the benefits of both elastic and inelastic materials while, at the same time, avoiding the disadvantages associated with these materials. As an example, there is a need for an elastic component that can be manufactured with both a thin wall and a small internal diameter. There is also a need for a small diameter, elastic sheath that can be quickly and inexpensively installed and used on a flexible insertion tube. Other medical devices and accessories would also benefit by such inexpensive, elastic, thin-walled components.
The present invention provides a method capable of forming thin-walled, elastic medical components from a heated, elastomeric sheet. The method of one particular embodiment of the invention may be used to manufacture small-diameter, thin-walled, elastic components, which has been problematic in the prior art. In an exemplary embodiment of the present invention, the method of forming a small-diameter, thin-walled elastic component includes heating a portion of the elastomeric sheet to a malleable temperature, pressing a distal end of an elongated forming tool on a first side of the elastomeric sheet at a location in the heated portion, stretching the heated portion with the forming tool until an elastic conforming portion is closely conformed to a portion of the forming tool, and removing the forming tool from the conforming portion of the sheet. The method of this embodiment can be used to form an elastic sheath having a thin wall, a small diameter, and a length shorter than the length of the insertion tube so that the elastic sheath may be stretched longitudinally over the insertion tube.
Embodiments of the present invention also provide a non-extruded thin-walled, elastic medical component made by the above-described process.